There is growing epidemiological evidence that asymmetric loading contributes to the increasing problem of low back pain in industry. The overall goal of the proposed research is to provide information that can contribute to reducing low back pain resulting from asymmetric loading, particularly twisting. The investigations will analyze the biomechanics of twisting and lateral bending. Experiments will be conducted in which biomechanical parameters will be measured in vivo. Using those data and refining currently available static biomechanical models, we will develop and validate a model that can be used to both predict and determine the tensions occurring in different trunk muscles during twisting and lateral bending and the associated forces acting on the lumbar spine. The model will be used to interpret existing guidelines and also to provide the scientific basis for further development of such guidelines. The specific objectives of the study are: 1. To experimentally analyze moments occurring in the lumbar spine during asymmetric loading, and to measure muscle activities of trunk muscles during these loads. 2. To refine the existing static trunk biomechanical models of lifting to reflect new data on, 1) muscle, tendon, ligament and bone geometry; 2) muscle function during load handling; and 3) dynamic lifting parameters estimated in research related to objected #1. 3. To validate the new trunk biomechanics model through experiments involving asymmetric, static and dynamic trunk loads while measuring trunk muscle myoelectric activity and estimating kinematic and kinetic parameters. 4. To compare spinal model output with existing published guidelines regarding lifting in various postures and asymmetric loading conditions, so as to interpret these and provide a more scientific basis for such guidelines in the future. The study will be carried out at two institutions: Rush-Presbyterian - St. Luke's Medical Center, Department of Orthopedics, Chicago, Illinois and the University of Michigan, Ann Arbor, Department of Mechanical Engineering and Center for Ergonomics, Ann Arbor, Michigan. The two institutions will work closely together, as they have in the past decade, with the main part of the experimental analysis taking part in Chicago and the main part of the model development being done at the University of Michigan.